Estimate of mating pattern of a paternal nest brooder goby of Rhinogobius, using egg density in the nest

Abstract

The mating pattern of the paternal nest brooder Rhinogobius sp. CB (cross band type) exhibits both monogamy and polygyny. However, it is difficult to infer the actual conditions of their mating from their egg stages in the clusters, because multiple females spawn simultaneously or sequentially within short intervals. I examined whether the egg density of the egg clusters could be used as an index of the number of females, based on laboratory and field experiments. Egg densities increased with the number of spawning females. Egg densities of egg clusters collected in the field were categorized into three normal distributions which corresponded to those for the number of mating females in the spawning experiment. Egg density in the nest, therefore, seems to be a useful index for clarifying the mating pattern of this species in the field. By adopting the present method, it is suggested that this species frequently mates polygynously in the wild.